2008 dudley pond circulator biomass report

Dudley Pond Circulator Evaluation Report – 2008 Weed Biomass Dudley Pond Circulator Evaluation Report 2008 Weed Biomass

By Toni Moores June 2009

Introduction This report contains the results of pond circulators impact on milfoil growth (biomass) in Dudley Pond for the 2008 growing season and contains conclusions, methods, results and a discussion of this experiment. This biomass growth experiment is a part of a two part evaluation program of pond circulators for the management of Eurasian Watermilfoil (milfoil) in Dudley Pond required by the Wayland Conservation Committee and funded by the Community Preservation Committee. The other part of this experiment deals with Pond water chemistry as it relates to pond circulators and was published in May of 2009.

The 2008 Dudley Pond Weed Biomass evaluation was essentially the same as in 2007 except that the Pond was treated with Sonar, an aquatic herbicide, on May 9, 2008.

It must be noted that there are a high number of uncontrollable variables which affect the data. These variables include wind direction and velocity, water depth, cloud cover, and height and density of the weeds. Unfortunately, then, it is highly unlikely that an accurate and meaningful assessment can actually be completed. The data provided here may or may not, then, prove meaningful.

Conclusions Based on the estimates of milfoil biomass gathered in May 14 and August 29, 2008, it does not appear that there was any difference in the milfoil biomass in the circulated areas of Dudley Pond versus the non-circulated areas of the Pond, with the herbicide Sonar in the water column.

Methods Other than the suggestion that we observe weed growth, the circulator vendor was unable to provide recommended procedures to methodically test the efficacy of the circulators.

In order to estimate the growth and rate of growth of milfoil, six, five foot squares of weighted 4” dia. PVC pipes were placed adjacent the circulators at various depths. See the Figure 1 below.   

Two squares (E1 and E4) at a depth of approximately 8 feet, Two squares (E2 and E5) at a depth water at approximately 10 feet and Two squares (E3 and E6) at a depth of approximately 12 feet.

Additionally six squares were placed in the control area (non-circulated area);  

Two squares (X1 and X4) at depths of approximately 8 feet, Two squares (X2 and X5) were placed in water of approximately 10 feet and 1

Dudley Pond Circulator Evaluation Report – 2008 Weed Biomass 

Two squares (X3 and X6) were placed at depths of approximately 12 feet.

Ropes with depth markers at one foot intervals and a buoy were attached to the PVC pipe squares. An attempt was made to locate the buoys approximately two feet below the surface, so that the weed squares could be located during each data gathering and to keep the buoys from interfering with boating on the Pond.

Figure 1 - Weed Square The placement of the weed squares in Dudley Pond appears in Figure 2 below.

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Dudley Pond Circulator Evaluation Report – 2008 Weed Biomass

Figure 2 – Approximate Locations of Circulators, Weed Squares & Sample Points In order to estimate the changes in weed biomass as a function of time, the number of milfoil plants within the PVC squares were counted at various time intervals and the height of the weeds were estimated to the nearest three feet. The total estimated lineal feet of weeds within the weed squares were used as an indirect estimate of biomass.

Digital videos of the weeds within the weed squares were made at various time intervals so that the physical appearance of the weeds could be evaluated.

On each data gathering occasion two divers were used to estimate the following within the weed squares; 1. Number of plants, 2. Number of stems with lengths between zero and three feet, 3. Number of stems with lengths between three feet and six feet and 4. Number of stems with lengths between six feet and nine feet.

The total number of lineal feet of weeds within the weed square was calculated to obtain an estimate of biomass for each weed square by each diver on each date. The gain or loss of biomass within the weed squares over the sampling interval in the circulated area versus the non-circulated area was assumed to represent the effect of the pond circulators.

To calculate biomass using this method, it was assumed that all of the stems with lengths less than three feet were three feet in length and all the stems between three and six feet were six feet in length and all of the stems with lengths greater than six feet were nine feet in length. If there were stems longer than nine feet they were assumed to have a length of one additional foot.

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Dudley Pond Circulator Evaluation Report – 2008 Weed Biomass To try to evaluate the impact of water depth on circulator performance an attempt was made to place weed squares  X1, X4, E1 and E4 in shallow water,  X2, X5, E2 and E5 in medium depth water and  X3, X6, E3 and E6 in deep water.

These placements allowed comparisons of circulated versus non-circulated biomass changes as function of depth.

Results 14-May Square X1 X2 X3 X4 X5 X6 E1 E2 E3 E4 E5 E6

29-Aug Spriglets # of Plants 0 0 14 4 1 1 5 4 14 4 13 5

Lineal Feet

208 450 285 ND 978 2353 609 ND ND 141 762 1671

4 13 6 0 33 2

3 14 9 0 28 2

Table 1 – Lineal Feet of Weeds within Weed Squares To see the physical conditions of the weeds in the weed squares visit: http://picasaweb.google.com/Wayland.SWQC/2008UnderwaterWeedSquareVideos14M AY08?feat=directlink

http://picasaweb.google.com/Wayland.SWQC/2008UnderwaterWeedSquareVideos29A UG08?feat=directlink There is a remarkable difference in the quantity weed biomass shown in the May 14 video versus the quantity of weed biomass shown in the August 29 video. The difference in weed biomass is due to herbicide having been applied on May 9, 2008.

Discussion The Pond was first treated with the herbicide Sonar on May 9, 2008. As can be seen in Table 1 the lineal feet of milfoil estimated at each weed square May 14, the milfoil were 4

Dudley Pond Circulator Evaluation Report – 2008 Weed Biomass off to a good start. Unfortunately the divers were not able to find weed squares X4, E2 and E3 due to the dense growth of weeds and algae during the May 14 weed count.

The second weed count was undertaken on August 29, 2008. Much of the biomass had been killed by the herbicide by that date. The method of counting the stems and estimating their height was not possible because so few milfoil plants were left standing, so the divers counted “spriglets” and the number of plants that had spriglets. To provide an insight regarding the conditions of the milfoil plants during the August 29th weed count the diver’s notes are included below.

All plants observed appeared to be bent over or darkened in stem. In only a couple instances did John observe plants that were above the 3 foot mark, so almost all counts are of spriglets on plants extending up a few inches to a couple feet off the bottom. Ted observed only one plant that had a spriglet over 2 inches in length at the end of its stalk.

John took videos, made counts that were just total number of spriglets, and obtained a depth to bottom. Depth to bottom was read from John’s Scuba depth gauge. Ted counted total number of spriglets, total number of plants, total number of plants with any spriglets, and in the circulator area counted total number of plants with no spriglets. An attempt was made to indicate the number of spriglets relative to the number of stems.

Mostly there were single stemmed plants with or without a spriglet. Where there were multiple stemmed plants, there were usually 2 or 3 spriglets per plant. Spriglets usually consisted of a single whorl of leaflets sticking out of a blackened stem. Some of the spriglets that came out of a node on the stem were so small (less than 1/8 inch across) they were hard to distinguish from the algae that was on the stems. This might account for some of the counting discrepancies. When they were on the end of a stalk, in rare instances there were multiple whorls of leaflets that may have totaled one half inch to 2 inches. No instances of spriglets coming directly out of the sediment surface were observed.

The data contained in Table 1 does not provide any indication that the pond circulators had an influence on milfoil when the herbicide Sonar was used. A visual comparison can be gained by viewing the underwater videos that were taken at the weed squares on May 14 and August 29, 2009.

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